Unless the sketch has the number 1, the word 
(letter) end (e), or the number is CIRCLED, it is 
NOT key.  [Circled numbered is usually the only 
way to ID mid-sequence key cels.]  However, you 
should pat yourself and others on the back for 
securing matching AIC sketches.

Most of the genga I've seen have both 'rough' 
drawings of the characters and the background, 
but it's kinda odd just seeing the background.  
If I had to guess, I would say you have a genga 
here.

You can take a look at my Yagami cel at the URL 
above for an example of my Tenchi cel with both 
matching douga and genga.  As soon as Yann sends 
me the OVA Sasami cel that he had in his shop, 
I'll show that one as an example as well.

Later.